Method and apparatus for microplasma spray coating a portion of a turbine vane in a gas turbine engine

ABSTRACT

A method and apparatus for microplasma spray coating a portion of a turbine vane without masking any portions thereof. The apparatus includes a microplasma gun with an anode, cathode, and an arc generator for generating an electric arc between the anode and cathode. An arc gas emitter injects gas through the electric arc. The electric arc is operable for ionizing the gas to create a plasma gas stream. A powder injector injects powdered material into a plasma stream. A localized area of the turbine vane is coated with the powdered material without having to mask the turbine vane.

CROSS REFERENCE TO RELATED APPLICATION(S)

The instant application is a divisional application of allowed U.S.patent application Ser. No. 10/976,560, filed Oct. 29, 2004, entitledMETHOD AND APPARATUS FOR MICROPLASMA SPRAY COATING A PORTION OF ATURBINE VANE IN A GAS TURBINE ENGINE.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to spray coating methods andapparatus and, more particularly, relates to a method and apparatus formicroplasma spray coating a turbine vane in a gas turbine engine.

BACKGROUND OF THE DISCLOSURE

Plasma coating methods and apparatus are known. For example, one patentrelates to a method and apparatus for plasma flame spray coatingmaterial onto a substrate. The patent discloses a method and apparatusfor plasma flame spray coating material onto a substrate by means ofpassing a plasma forming gas through a nozzle electrode, and passing anarc forming current between the nozzle electrode and a rear electrode toform a plasma effluent. The method includes introducing coating materialinto the plasma effluent, passing the plasma effluent axially through awall shroud extending from the exit of said nozzle electrode, andforming a flame shroud for the plasma effluent. The coating is therebyapplied to the substrate.

One area where such technology is particularly advantageous is inconnection with coating various aircraft components, particularly gasturbine engines and their components. For example, the turbine vanes canbe coated with material to meet dimensional tolerance requirements forsealing the flow path adjacent the turbine vane. Metallic coatingsconsisting of nickel chrome alloy, nickel chrome-chrome carbide, andother similar composition materials have been applied in this regardusing various conventional plasma spray coating processes. Typically,the coating process requires the turbine vane to be masked in areaswhere the material transfer is not required and/or not desired.Furthermore, the turbine vane is typically coated in a dedicatedfacility such as an aircraft engine manufacturing plant or repair shop.Prior art methods and apparatus required masking the turbine vane andapplying the coating in dedicated facilities because the coatingequipment was large and not portable and the spray pattern was too wideto accurately control the coating process. It would be desirable toimprove the accuracy of spray coating devices so that masking and thelike would not be required, as well as permitting hand spray coatingrepairs in the field of operation.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the disclosure, a microplasma sprayapparatus for coating at least a portion of a turbine vane is provided.A microplasma gun includes an anode, cathode, and an arc generator forgenerating an electric arc between the anode and cathode. The apparatusincludes an arc gas emitter for injecting gas into the electric arc. Theelectric arc is operable for ionizing the gas to create a plasma gasstream. A powder injector injects powdered material into the plasma gasstream. The turbine vane can be coated in a localized area with thepowdered material without masking the turbine vane.

In accordance with another aspect of the present disclosure, a methodfor microplasma spray coating a turbine vane is provided. The methodincludes providing a microplasma spray gun having an anode and cathodeand means for generating an electric arc between the anode and thecathode. Inert arc gas is injected through the electric arc to ionizethe gas and form a plasma gas stream. Powdered material is injected intothe plasma gas stream. The method provides for coating a localized areaof a turbine vane with the powdered material without masking the turbinevane.

In accordance with another aspect of the present disclosure, a methodfor repairing a turbine vane using microplasma spray coating isprovided. The turbine vane can be repaired with the microplasma spraycoating in an operating field without utilizing a dedicated spraycoating facility in a manufacturing environment. A hand controlled andoperated microplasma gun is utilized for applying the coating. Inert arcgas is injected through an electric arc generated by the microplasmaspray gun. The inert gas is ionized with the electric arc to form aplasma gas stream. Powdered material is injected into the plasma gasstream which coats a localized area of the turbine vane without maskingportions of the turbine vane.

Other applications of the present invention will become apparent tothose skilled in the art when the following description of the best modecontemplated for practicing the invention is read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representing a microplasma spray gun and aworkpiece;

FIG. 2 is an exploded, perspective view of a microplasma spray apparatusconstructed in accordance with the teachings of the disclosure;

FIG. 3 is a perspective view of the microplasma spray apparatus of FIG.1, applying a coating to a workpiece; and

FIG. 4 is a flowchart describing the process for coating the microplasmaspray coating a workpiece without masking.

While the following disclosure is susceptible to various modificationsand alternative constructions, certain illustrative embodiments thereofhave been shown in the drawings and will be described below in detail.It should be understood, however, that there is no intention to limitthe disclosure to the specific forms disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the disclosure asdefined by the appended claims.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now to FIG. 1, a microplasma spray apparatus 10 schematicallyrepresented by the dashed box outline is depicted. In generalized terms,the microplasma spray apparatus includes a microplasma gun 12 having anarc gas emitter 14, an anode 16, and a cathode 18. An electric arc 20 isgenerated between the anode 16 and cathode 18. A plasma stream 21 isformed when arc gas is injected from the arc gas emitter 14 through thearc 20. A powdered material injector 22 dispenses powdered material intothe plasma stream which transports the powdered material to theworkpiece 24. As a result, the powdered material forms a coating with athickness of approximately 0.003 to 0.006 inches in a desired locationon the workpiece 24.

While a number of different embodiments and structural variations can beconstructed to practice such an invention, the following describes onecurrently known embodiment. Referring now to FIG. 2, an exploded view ofsuch a microplasma spray apparatus is again referred to by referencenumeral 10. As will be described in detail below, the microplasma sprayapparatus 10 is operable for coating many things, including, but notlimited to at least a portion of a turbine vane 72 in a gas turbineengine (not shown). However, it is to be understood that the teachingsof disclosure can be used to coat myriad other surfaces, including thoseon aircraft, land-based vehicles, weapons, sea-faring vessels and thelike.

In the depicted embodiment, the microplasma spray apparatus 10 includesthe aforementioned microplasma gun 12 having an anode 16 and a cathode18. The cathode 18 is further depicted to include an insulated body 26with an electrode 28 extending therefrom. The cathode 18 can alsoinclude threads 30 for threadingly engaging the microplasma gun 12. Thecathode 18 can also include an O-ring seal 32 to seal the leak path thatis created at the interface between the cathode 18 and the microplasmagun 12.

In operation, an electric arc 20 (FIG. 1) is generated between the anode16 and cathode 18 of the microplasma gun 12. Arc gas such as, but notlimited to argon, is emitted into the electric arc formed between theanode 16 and the cathode 18. It should be understood that in practicethe arc gas can be emitted prior to generating the electric arc. Theelectric arc ionizes the gas to create the plasma gas stream 21. Theionization process removes electrons from the arc gas, causing the arcgas to become temporarily unstable. The arc gas heats up toapproximately 20,000° F. to 30,000° F. as it re-stabilizes. The plasmastream cools rapidly after passing through the electric arc.

A powdered material injector 22 injects powdered material 34 into theplasma gas stream 21. The powdered material 34 is heated and superplasticized in the plasma stream and is deposited on the turbine vane 72where it cools and re-solidifies to form the coating. The powderedmaterial injector 22 includes a powder hopper 36 for holding thepowdered material 34. The hopper 36 is attached to the microplasma gun12 via a connector 38 formed on the microplasma gun 12. The powderhopper 36 holds powdered material to be sprayed onto the turbine vane72. The powdered material 34 is channeled through a discharge chute 40and controlled by a valve 42 positioned in the discharge chute 40. Thevalve 42 can be mechanical or electromechanical as is known to thoseskilled in the art. Powder may also be injected into the plasma streamvia a powder gas line from a standard powder feeder (not shown).

A nozzle shroud 46 positioned on a forward wall 48 of the microplasmagun 12 holds a nozzle insert 50 and permits the electrode 28 to extendthrough a center aperture 52 formed in the nozzle shroud 46. The nozzleinsert 50 can be threadingly attached to an end of the nozzle shroud 46.A shield gas cap 54 is positioned adjacent the nozzle shroud 46. Aninsulator 56 is positioned between the shield gas cap 54 and the nozzleshroud 46 to electrically isolate the shield gas cap 54 from the nozzleshroud 46. The shield gas cap 54 can be pressed to fit onto the nozzleshroud 46 and over the insulator 56. The shield gas cap 54 includes aplurality of through apertures 58 for permitting shield gas to flowtherethrough and shield the arc gas from ambient atmosphere. A centeraperture 60 formed in the shield gas cap 54 permits high velocity arcgas to pass through and into the electric arc.

Cooling fluid, such as water or the like, is utilized to cool themicroplasma gun 12. The cooling fluid is delivered to the microplasmagun 12 via a cooling fluid hose 62. The cooling fluid traverses throughinternal passages (not shown) in the microplasma gun 12 and flowsthrough an inlet passage 64, into an anode holder 66 and back through anoutlet passage 68. The cooling fluid reduces the temperature of theanode 16 during operation of the microplasma gun 12. The cooling flowrate may be approximately 1.0-1.5 gallons per minute. A second conduit70 is connected to the microplasma gun 12. The second conduit may beoperable for providing electrical power, arc gas, and shield gas to themicroplasma gun 12.

Referring now to FIG. 3, it is shown that a localized area of theturbine vane 72 such as a rail 74 can be spray coated with powderedmaterial 34. The plasma gas stream 21 is directed toward the portion ofthe turbine vane 72 to be coated. The microplasma gun 12 is operated ata relatively low power range of between approximately 0.5 Kilowatts and2.5 Kilowatts. The low power output of the microplasma gun 12significantly reduces the heat flow into the turbine vane 72 over thatof conventional coating methods. The maximum surface temperature of theturbine vane 72 caused by the coating process is approximately 200° F.depending on the size of the vane. The microplasma gun 12 is operablefor applying powdered material 34 to a thin wall area of the turbinevane 72 without distorting the turbine vane 72 because the low poweroutput limits the localized stress caused by high thermal gradients.

The microplasma gun 12 can apply coating material in narrow strips ofapproximately 2 mm in width. This permits accurate surface coating evenwith a hand held device. The narrow strips of coating substantiallyeliminate the need for masking or otherwise covering the turbine vane 72in areas where the coating is unwanted. The narrow spray pattern iscontrolled by the nozzle opening size. The hand held version of themicroplasma gun 12 is so accurate that coating can be sprayed oncomponents while they remain installed in an engine or the like.

The arc gas flow rate of the microplasma apparatus 10 may be betweenapproximately 1.5 and 3 liters per minute. As stated above, the arc gasand shield gas are typically argon, but any suitable inert gas can beutilized as is known to those skilled in the art. The shield gas flowrate ranges between approximately 2 and 4 liters per minute for atypical application. The coating material for the turbine vane 72 can bea chrome carbide alloy, nickel chrome alloy, or other high temperaturealloys suitable for turbine vanes having operating temperatures that aretypically above 2000° F., as is known to those skilled in the art.

The powder hopper 36 holds the powdered material 34 prior to beinginjected into the plasma gas stream 21 by the powder injector 22. Thepowdered material 34 can be injected into the plasma gas stream 21either through gravity feed or through a pressurized system (not shown).The shut-off control valve 42 controls the powdered material 34 feedrate into the plasma gas stream 21. Powdered material 34 is transferredto the turbine vane 72 from between approximately 1 to 30 grams perminute. The microplasma gun 12 can typically apply the coating fromdistances ranging from approximately 1.5 inches to 6.5 inches to theturbine vane 72, but can vary depending on the coating applicationrequirements. The microplasma spray gun 12 can be oriented between apositive 45° angle and a negative 45° angle relative to a normal axis ofthe turbine vane and still provide adequate material coating with agravity feed system. A pressure feed system provides unlimited angles oforientation for the microplasma gun 12. The microplasma spray gun 12generates a relatively low noise level that ranges from between 40 and70 decibels due to the low power output, thereby making the apparatus 10suitable for hand held application. Current U.S. government regulationsrequire hearing protection when environmental noise reaches 85 decibels.The microplasma spray apparatus 10 can be hand held or alternativelyheld in an automated fixture (not shown) that is computer controlled.

Referring now to FIG. 4, a block diagram generally describing theoperation of the microplasma spray apparatus 10 and the plasma spraycoating process is illustrated. Initially, at block 80, arc gas isemitted from the nozzle insert 50. An electric potential is generatedbetween the anode 16 and the cathode 18 of the plasma spray gun 12 andis directed through the arc gas, as described in block 82. Arc gas isdirected through the electric potential to create the plasma stream 21.At block 84, powdered material 34 is injected into the plasma stream 21.At block 86, the plasma stream is heated the powdered material 34 to“super plasticized” condition such that the powdered material 34 ismalleable when it is applied to a workpiece. At block 88, the powderedmaterial 34 is applied to an unmasked substrate. The powdered material34 then cools and solidifies as a hard coating on the substrate.

While the preceding text sets forth a detailed description of certainembodiments of the invention, it should be understood that the legalscope of the invention is defined by the claims set forth at the end ofthis patent. The detailed description is to be construed as exemplaryonly and does not describe every possible embodiment of the inventionsince describing every possible embodiment would be impractical, if notimpossible. Numerous alternative embodiments could be implemented, usingeither current technology or technology developed after the filing dateof this patent, which would still fall within the scope of the claimsdefining the invention.

What is claimed is:
 1. A method for microplasma spray coating a turbinevane, comprising: providing a microplasma gun including an anode, acathode including an electrode extending therefrom and disposed throughan aperture in a nozzle, said anode being disposed opposite said cathodewithin an anode holder mounted to an exterior surface of saidmicroplasma gun, and means for generating an electric arc between theanode and the cathode; injecting inert arc gas from said nozzle;ionizing the arc gas with the electric arc to form a plasma gas stream;injecting powdered material into the plasma gas stream; and coating alocalized area of the vane with the powder material without masking thevane.
 2. The method of claim 1, further including operating themicroplasma gun at a relatively low power range between approximately0.5 Kilowatts and 4 Kilowatts.
 3. The method of claim 1, furtherincluding applying the coating material to the vane without causingdistortion of the vane.
 4. The method of claim 1, further includingapplying the coating material to the vane in narrow widths ofapproximately 2 mm.
 5. The method of claim 1, further including flowingthe arc gas at a rate between approximately 0.5 and 3 liters per minute.6. The method of claim 1, further including flowing the shielding gas ata rate between approximately 2 and 4 liters per minute.
 7. The method ofclaim 1, further including feeding the powder material at a rateapproximately between 1 and 30 grams per minute.
 8. The method of claim1, further including cooling the microplasma gun with a water coolingsystem.
 9. The method of claim 1, further including applying the coatingto the vane from a distance of between approximately 1.5 to 6.5 inches.10. The method of claim 1, further including applying the coating to thevane with the microplasma gun angle positioned approximately between apositive 45 degree angle and a negative 45 degree angle relative to anormal axis of the part.
 11. The method of claim 1, further includinggenerating a noise level of between approximately 40 and 70 decibelsduring operation.
 12. A method for repairing a turbine vane in a gasturbine engine using a microplasma spray coating apparatus comprising:using a hand controlled and operated microplasma spray gun; injectinginert arc gas through an electric arc generated by the spray gun;ionizing the arc gas with the electric arc to form a plasma gas stream;injecting powdered material into the plasma gas stream; and spraycoating a localized area of the turbine vane with the powdered materialwithout masking the turbine vane and without utilizing a dedicated spraycoating facility.
 13. The method of claim 12, further includingoperating the microplasma gun at a relatively low power range betweenapproximately 0.5 Kilowatts and 2.5 Kilowatts.
 14. The method of claim12, further including applying the coating material to the vane withoutcausing distortion of the vane.
 15. The method of claim 12, furtherincluding applying the coating material to the vane in narrow widths ofapproximately 2 mm.
 16. The method of claim 12, further includingflowing the arc gas at a rate between approximately 1.5 and 3 liters perminute.
 17. The method of claim 12, further including flowing theshielding gas at a rate between approximately 2 and 4 liters per minute.18. The method of claim 12, further including feeding the powdermaterial at a rate approximately between 1 and 30 grams per minute. 19.The method of claim 12, further including cooling the microplasma gunwith a water cooling system.
 20. The method of claim 12, furtherincluding applying the coating to the vane from a distance of betweenapproximately 1.5 to 6.5 inches.
 21. The method of claim 12, furtherincluding applying the coating to the vane with the microplasma gunangle positioned approximately between a positive 45 degree angle and anegative 45 degree angle relative to a normal axis of the part.
 22. Themethod of claim 12, further including generating a noise level ofbetween approximately 40 and 70 decibels during operation.